SUMMARY The goal of this project is to understand how protein quality control mechanisms in adult stem cells and theirprogenyareregulatedduringaging,withtheobjectivetorestorethefunctionalityofoldcells.Preservation of a pristine proteome is emerging as a critical mechanism for maintaining cellular function throughout life. Disruption in the machinery that maintains protein quality control leads to protein aggregation diseases and accelerated aging in invertebrate models. However, how cell types with different roles regulate protein homeostasisduringlongperiodsoftimeremainsunexplored,particularlyinmammals.Theadultbrainoffersa uniqueparadigmforunderstandingproteinqualitycontrolmechanismsincelltypeswithdifferentfunctions.It containsreservoirsofquiescentneuralstemcells(NSCs)thatcanactivateandinturngeneratedifferentiated cellswithspecializedfunction?neurons,astrocytes,andoligodendrocytes.Duringaging,theabilityofNSCsto exitquiescenceandtheirabilitytoproducenewneuronsbothdeclinedramaticallyyetthisdeteriorationisnot inexorableandcanbereversedbyenvironmentalinterventions,includingdiet.However,themechanismsthat canregulateNSCfunctionarelargelyunknown. We recently embarked on a systematic characterization of protein aggregates and proteostasis mechanisms in young NSCs and their progeny. Excitingly, we find that quiescent NSCs contain large protein aggregatesthatarepresentundegradedinlargelysosomes.Nutrientdeprivationcanclearproteinaggregates and enhance their ability to activate, a process that is dramatically affected by aging. Interestingly, our RNA- seq profiling from young and also mice reveal that quiescent NSCs from old mice exhibit a large degree of transcriptome-wide change with age. The central hypothesis of this Project is that the protein quality control mechanisms differ in cell types with distinct functions, which could underlie their different degree of deterioration with age and could be used for specifically ameliorating old cells. To test this idea, we propose thefollowingexperiments: 1. To understand how protein aggregates and protein quality control mechanisms are influenced by increasingageandbyrejuvenatingstrategies 2. To specifically modulate proteostasis mechanisms to ameliorate function in old NSCs and their differentiatedprogeny 3. To determine the composition of protein aggregates and generate new aggregate reporters in NSCs andtheirprogeny CompletionoftheseAimswillprovideuniquemechanisticinsightsintotheregulationofproteinaggregates and their alteration during aging in regenerative cells and their differentiated progeny. This study should also provide fundamental understanding of how protein quality control is mechanistically regulated in different cell types.Thisknowledgeshouldpavethewayforbuildingnewmethodsfor?rejuvenation?ofoldcellsandrestore protein aggregates, which will be a critical step for improving tissue function during aging and age-related disease.